1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method. More specifically, the invention relates to processing of image data temporarily stored in a hard disk of an multi-function combined machine so that duplication and alteration thereof may be inhibited using a copy-forgery-inhibited pattern.
2. Description of the Related Art
Conventionally, in order to inhibit or restrain copying of a document, a resident card, and the like, contents of them have been printed on a paper that has been subjected to special printing, called a forgery prevention paper. This forgery prevention paper is a kind of paper such that, in the case where the paper after printing is copied using a copier or the like, characters “Copy inhibited” or the like will emerge on the paper, although the characters on the original are hard for humans to recognize with an eye. The paper gives rise to an effect that may make people who copies hesitate to use its duplication or doing similar things. Further, the paper also gives rise to an effect that copying itself is inhibited or restrained because such a document etc. is printed on the forgery prevention paper.
However, such forgery prevention paper comes with a problem of being high cost as compared with normal papers. Moreover, the forgery prevention paper can makes only characters that were set at the time of manufacturing emerge, which accordingly limits applications of that paper, and the like; therefore, such paper lacks in flexibility in terms of usage.
On the other hand, while digitization of various contents the flow proceeds, contents of documents, the resident card, and the like are digitized similarly. However, digitization of these documents and the resident card themselves are still in a transition stage, and in many cases contents made by computes are outputted on papers using a printer and then used.
Under such a situation like this, there is known a technology of manufacturing the forgery prevention paper that has heretofore been created by plate making etc. using a computer and a printer (Japanese Patent Application Laid-open No. 2001-197297). This is a technology whereby, when contents created using a computer is printed out, image data called a copy-forgery-inhibited pattern is generated and this data in addition to data of the contents are superposed and outputted. The copy-forgery-inhibited pattern is occasionally called a copying restraining pattern. Although the copy-forgery-inhibited pattern image is seen as a simple pattern, a background image, or the like to an eye of a human in an original print (printed matter outputted from a printer), once it is copied, predetermined characters or an image will be visualized. This original can give the same restraining effect as the above-mentioned forgery prevention paper. This has been made possible thanks to remarkable improvement of the printer.
In the case where the copy-forgery-inhibited pattern image created using a computer is superposed on contents data and outputted, since naturally normal printing papers etc. can be used to output the contents, this case is advantageous in terms of cost as compared with the case of using the previously created forgery prevention paper. In addition, since the copy-forgery-inhibited pattern image can be created when contents are printed out, it becomes possible to freely determine characters to be visualized at the time of copying the original as well as a color of the copy-forgery-inhibited pattern image. Alternatively, this method also has an advantage that printing time and data, information specific to printing equipment or the like can be drawn as the copy-forgery-inhibited pattern image.
The copy-forgery-inhibited pattern image exerts an effect of, when copying an original, restraining the use of a duplication of the original by visualization of predetermined characters etc. that cannot be recognized before copying, as described above. In order to realize this effect, any copy-forgery-inhibited pattern image basically consists of two areas: one area where the same image as that of the original remains also in the duplication; and one area where an image disappears or becomes thin as compared with the image in the above-mentioned remaining image area, in the duplication. Regarding the copy-forgery-inhibited pattern image consisting of these two areas, what is suitable is one that the above-mentioned two areas are specified to have almost equal density when the copy-forgery-inhibited pattern has been printed out. That is, the copy-forgery-inhibited pattern image that is printed out is composed in such a way that in a macro sense, characters to be visualized on its duplication are hard to recognize visually by humans. In the following description, an image area that is hidden in a printed-out matter of this copy-forgery-inhibited pattern image but will be emerged visually recognizable by humans in the duplication that is copied from the printed-out matter is referred to as a “latent mark (or the latent-mark), while an image area that will disappear by copying or will become a low density as compared with the density of the latent mark having visualized on the duplication is referred to as a “background image (or the background).” Any copy-forgery-inhibited pattern image basically consists of these latent marks and background images. Note that the latent-mark is often called a foreground as a terminology used for the user interface.
The latent mark is so composed that dots are concentrated in a predetermined area. Contrarily, the background part is so composed that dots are dispersed in a predetermined area. Further, the copy-forgery-inhibited pattern image can be so composed that densities of the two areas are almost equal to each other, and consequently the latent-mark part and the background part are made hard to distinguish from each other in a printed-out matter of the copy-forgery-inhibited pattern image.
FIG. 1 is a diagram showing the states of dots in the two image areas, respectively. As shown in the figure, a copy-forgery-inhibited pattern image is constructed with the background part where dots are arranged being dispersed in a predetermined area and the latent-mark part where dots are arranged being concentrated. The dots in these two areas can be generated by mutually different halftone dot processing or mutually different dithering processing. For example, in the case of creating a copy-forgery-inhibited pattern image using the halftone dot processing, the latent-mark part is subjected to the halftone dot processing with a low number of lines. It is preferred that the background part is subjected to the halftone dot processing with a high number of lines. In the case where a copy-forgery-inhibited pattern image is created using dithering processing, the latent-mark part is subjected to the dither processing using a dot concentrated type dither matrix. It is preferred that the background part is subjected to dither processing using a dot dispersed type dither matrix.
Generally, the reading unit and the image forming unit of the copy machine has a limit level of reproduction capability that depends an input resolution whereby micro dots in a manuscript image is read and an output resolution whereby micro dots are reproduced. If the dot in the background part of the copy-forgery-inhibited pattern image is formed smaller than the limit level of dot reproducible by the copy machine and the dot in the latent-mark part is formed larger than the limit level, the dots of the latent-mark part are reproduced and the small dots in the background part are not reproduced on the duplication. By utilizing such property, the latent-mark is visualized on the duplication that inevitably copied the copy-forgery-inhibited pattern image. Hereafter, an image that is visualized on the duplication is called a visualized image. Note that even if the background part is reproduced by copying, but if the latent-mark part on the duplication is in an apparently recognizable level, the same effect as when the dots in the background part are not reproduced can be obtained, which is as described above.
FIGS. 2A and 2B are the diagrams showing this visualization. The figures indicate conceptually that when the dots are concentrated, the image is visualized also on the duplication, whereas when the dots are dispersed, the image is not reproduced on the duplication.
It should be noted that the copy-forgery-inhibited pattern printing is not restricted to the above-mentioned composition, but it may have any composition as long as a character string etc. is reproduced in a conceivable level on the duplication. That is, if a character string etc. is specified as the background part and will be shown in the state of a white character after copying, the purpose is attained as copy-forgery-inhibited pattern printing.
The copy-forgery-inhibited pattern image as described above finds its application in various environments. Usually, print data of a manuscript image with a copy-forgery-inhibited pattern image added thereon is created in a host computer and sent with a printing direction etc. to a printing apparatus, such as a printer, to perform printing. On the other hand, there is known a printing apparatus that temporarily stores image data being read by a scanner and image data sent from the host computer via a network in a storage device, such as a hard disk. Then, the printing apparatus reads arbitrary data from among pieces of the image data stored in this way and prints it out. Many of such printing equipment are known as forms of the multi-function combined machine. Larger capacity of hard disk makes it possible for this combined machine to accumulate therein a large amount of the image data, which makes it practical to use the digital combined machine as the so-called image server. For example, a single multi-function combined machine performs editing processing of image date, such as copying the image data saved in the hard disk and deleting unnecessary pages of data consisting of two or more pages, without using a computer. Moreover, it is commonly done to display the image data on a display unit of the multi-function combined machine and to send the image data to other device via a network and print it there (Japanese Patent Application Laid-open No. 2005-111957).
However, copy-forgery-inhibited pattern image data or processing regarding it is done assuming a case where the copy-forgery-inhibited pattern image data is printed, as it is, and it exerts a function of the copy-forgery-inhibited pattern image when it is copied. For this reason, the conventional processing does not take into consideration existence of possibility that the function of the copy-forgery-inhibited pattern image is not fully exerted, such as damaging of the copy-forgery-inhibited pattern image or lowering of guaranteed level of the original, in the case when the image data temporarily stored in the hard disk etc. is first used for processing other than printing.
For example, in the case where image data with a copy-forgery-inhibited pattern image added therein is read from a hard disk and sent to other equipment, processing of decreasing data quantity for reduction of network load and/or that of adjusting the image data to be transmitted to a capacity of equipment at a transmission destination site is performed. For this purpose, image processing, such as resolution transformation, may be performed on the image data. In this case, it may occur that a pattern constituting the copy-forgery-inhibited pattern image is collapsed to become an abnormal image, such as generating jaggy. Even when the image does not become an abnormal image, the image may be printed with no copy-forgery-inhibited pattern emerged in equipment at the transmission destination site. In such cases, the effect of restraining illegal duplication by addition of a copy-forgery-inhibited pattern will be lost. Moreover, not a case where the image data is sent to other equipment, there is a case where in the multi function combined machine saving the image data, the image with a copy-forgery-inhibited pattern added is displayed on a display that is provided therein. Even in this case, the stored image data for printing is altered to data for displaying, whereby a function of a copy-forgery-inhibited pattern is impaired similarly.
Further, there is also a case where image data with a copy-forgery-inhibited pattern image added thereon stored in a hard disk etc. is duplicated, falsified, or processed in other way in the multi-function combined machine. To stand against this, countermeasures of protecting any access to the multi-function combined machine by password, protecting accesses to respective accumulated data by pass word, and the like are being taken. However, it is generally difficult to prevent illegal duplication, falsification, etc. of an image without asking a user for troublesome operations, such as entering a password. Moreover, there is a case where although access to image data with a copy-forgery-inhibited pattern image added in an multi-function combined machine is protected, any restriction is not imposed on document editing functions (document duplication, document merging, document insertion, page deletion, etc.) that the multi-function combined machine is equipped with. In this case, if image data with a copy-forgery-inhibited pattern image added is duplicated, or falsified, or processed using the editing function, it becomes difficult to determine whether the document is a duplicated one. That is, it becomes difficult to guarantee that the image data with a copy-forgery-inhibited pattern image added is the original.
In addition, even in the case where the image data stored in a hard disk etc. of an multi-function combined machine is not image data with a copy-forgery-inhibited pattern image added but the normal image data, it is not desirable to allow it to be duplicated and falsified. Therefore, it is necessary to prevent duplication, falsification, etc. also for the normal image data.